A number of integrated circuits is currently available that include stepper motor controllers for various applications. One example is the L6226 DMOS driver for bipolar stepper motors of STMicroelectronics (see STM, L6228 DMOS driver, product information and data sheet, September 2003). Motor coils are typically driven using a H-bridge of power transistors. The H-bridge is composed of two half-bridges, and the coil is connected between the respective outputs of the two half-bridges. Thus the current through the coil can be controlled in both directions.
As can be seen from the datasheet mentioned above, it is common to include a kind of over-current protection into the motor controller in order to protect the controller and other components from thermal destruction due to short-circuits or the like. Upon detection of an over current the motor controller usually switches off the current and may signal an error.
In many applications, in particular in automotive applications, it may be desired to localize the cause of the over-current as this may significantly reduce the efforts which are necessary to fix the problem if over-currents occur. Thus there is a need for a motor controller which provides over-current protection that allows the localization of the cause responsible for the over-current.